This invention relates to a compound represented by the formula: ##STR00001## wherein M is selected from groups 3 11 of the periodic table; ##STR00002## L.sup.1 represents a formal anionic ligand, L.sup.2 represents a formal neutral ligand, a is an integer greater than or equal to 1; b is greater than or equal to 0; c is greater than or equal to 1, E is nitrogen or phosphorus, Ar.sup.0 is arene, R.sup.1 R.sup.4 are, each independently, selected from hydrogen, hydrocarbyl, substituted hydrocarbyl or functional group, provided however that R.sup.3 and R.sup.4 do not form a naphthyl ring, N is nitrogen and O is oxygen.This invention further relates to a process to oligomerize and/or polymerize unsaturated monomers using the above compositions, optionally combined with an activator.